Pulse direction finder system



5 Sheets-Sheet l illl'f Filed Deo IN1/T0125 E B. Isl-IMURAK Er AL PULSEv DIRECTION FINDER SYSTEM AMAA;

July 8, 1947.

B. SHMURAK El' AL PULSE DIRECTIN FINDER SYSTEM Filed Dec. 30. 1945 5 Sheets-Sheet 2 'rmer/afuera@ CEI/TEK .WHW/V6 PULSE July s, 1947. a SHMURAK Er AL 2,423,523

PULSE DIRECTION FIINDER SYSTEM Filed D60. 30, 1943 3 Sheets-Sheet 3 q& u @LA fr d'7/7 F1957 me-5P INVENTORS. 5

Afro/mfr atented .luly 8, i947 STATES PATENT OFFICE PULSE DEB/ECTION FINDER SYSTEM Application December 30, 1943, Serial No. 516,196

4 Claims.

Our invention relates to receiver apparatus for identifying radio pulses and particularly to apparatus for use in radio pulse direction nder systems.

A disadvantage of direction nders of the usual type that obtain a bearing from a radio broadcast station or the like which transmits a continuous carrier wave is that, due to reilections, the carrier wave may travel several different paths in reaching the direction finder receiver. In systems of this type, it is dilcult, if not impossible, to distinguish the carrier wave that arrived by the most direct path from those that have arrived over paths that do not represent the true direction.

A radio pulse direction finder, on the other hand, may be designed to give separate indican tions of the direct pulse and the reflected pulses whereby the loop antenna or other directive receiving antenna may be rotated to the null position for the direct pulse.

Our invention will be described by way of example as applied to a pulse direction finder receiver designed to obtain a bearing from any one ol' a group of radio pulse transmitters of a radio navigation system. In this particular navigation system the transmitters are in groups of two, the two stations being identiiied as the A station and the B station and the pulses which are transmitted therefrom being identined as the A pulses and B pulses, respectively. The A and B stations of one group transmit pulses at the same repetition frequency. The A and B stations of another group transmit pulses at a second and different repetition frequency, this second repetition frequency also being the same for the A station as for the B station. All transmitter stations operate on the same carrier frequency.

An object of the present invention is to prou vide an improved receiver circuit for distinguishing a pulse that has been transmitted over one path from a pulse that has been transmitted over a diiferent path.

A further object of the invention is to provide a direction iinder having an improved deflecting circuit for the cathode ray pulse indicator tube.

A further object of the invention is to provide in a direction iinder, a simplied cathode ray deecting circuit for producing both a slow sweep and a fast sweep of the cathode ray.

A still further object of the invention is to provide an improved means for identifying either one of two stations that are operating on the same (Cl. Z50-11) 2 carrier wave and which are transmitting radio pulses that occur at the same repetition rate.

In practicing one preferred embodiment of the invention, a loop antenna picks up the radio 5 pulses from a transmitter station and supplies them through a suitable receiver and ampliiier to the vertical defiecting plates of a cathode ray indicator tube. The horizontal deflecting plates of the cathode ray tube have a sawtooth voltage wave applied thereto which is made to recur at the repetition rate of the incoming pulses whereby the pulses are caused to appear stationary on either a slow or a fast cathode ray trace.

A comparatively slow sweep is required for a fast sweep is required for good separation of pulses arriving by different paths. The two sweeps are provided as follows. The sawtooth deecting wave is given the usual Wave form whereby it has a fast return-line portion. During the occurrence of this return-line portion, a rectangular voltage pulse of the same duration as that of the said portion is applied to the vertical deflecting plates to displace the fast returnline trace with respect to the slow trace. In the example illustrated, the fast trace appears below the slow trace.

In operation, the sawtooth or sweep frequency 1s first adjusted to make the pulses appear on the slow sweep trace. Then the pulses are allowed to drift onto the fast sweep trace, the drift being due to the fact that the sawtoothirequency is not made exactly synchronous with the pulse repetition rate. When the pulses appear on the fast sweep, the sawtooth frequency is made exactly synchronous with the pulse frequency whereby the direct pulse and the echo pulses are stationary and, due to the fast sweep, are well spaced so that the desired pulse may be observed while obtaining a null for indicating direction in the conventional manner.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure 1 is a circuit diagram of one embodiment of our invention,

Figure 2 is a circuit diagram of an oscillator that may be employed in the circuit of Fig. 1,

Figures 3 through 8 are graphs that are reease of locating the pulses on the sweep whereas 1 1 1 The horizontal deilectfing-plates: liand; ld arefy 1 1 1 suppliedwi'th -sawtooth voltages indicated at: iid

' .and llo ffrom. amplifier tubes 1418 and: i9,11respec1 1 which iis coupled .to a `second vacuum1 tube 52 1 :througha: coupling capacitor .53.' 1. The. anode of 1 1 1 1 1 1 1 1 1 Figure ad a 1view: corresponding to Fig. il but 1 f 1 :fori the .condition .where 1 the pulses have been; 1

1 1 1 1 drifted vonto the fast :sweep trace,1 and 1 1 l.

1 1. 1 1 1 Figures 19. to 1105i are1 other graphs that; 1

I 1 tively,- which amplify thesaiwtooth Voltage: il api 1 1,

. 1 i 1peering. across a :potentiometer resistor 2i to 1 1 1 which 1an input.1 lead 1221is =connected.z 1 1t will be 1 1 :noted that 1 the :tube 1h31 reverses the :polarity1 :ci 1 2 1 i :the sau/tooth wave 1 il. 1 Suitable :centering bii 1 1 .ases are supplied. tothe cathode ray'tube chest-1 1 1 1 ing plates through: 11.5: megohm; resistors. as indi- 1 ca1ted. i 1.1` 1:`;

1 f f Rectangular puiseisindicated at .23 are supplied 1 1 1 1 .over :ag conductor 12a to; 'the .vertical :deflectin'g 1 1 aaeaaea :are also supplied to a :vertical deecting plate.;

r Theipulse's 5a are obtaineclby passing the Ipulses 1 I f 1 1 1 1 1 13d, appearing at the anode of the tube 1 321,1 1 1 l through a1 small-'capacitor andover a conclue- 1 1 :tor :65 toi the grid of tube 481.1 The capacitor 155: 1 1 1 1 referredto in explaining the invention: 11 1 .51 n 1-.In1the several iiguressimilar parts and graphs. 1.1is. small enough to` differentiatethe pulses lill;` fare indicated by similar reference characters.1 1 The 1 pulses corresponding to theA backA edges 10i 1 1 .1; 1 Referring. tolrig i. the radio1 .pulses -frorn a. 1:puisesz are' :mixed with the pulses 1231as shown 1 .1 *transmitterrare picked up by-a loop antenna in. in Fig.` The time. relations ofthe voltages/aves1.11 .1

. a streamline housing E@ and supplied to a reoeiv; 101 121:6, H1 and 231 with respect to each other and 1 1 1 1 er; and` detector-unit 1i l1 and to a video frequency 1 1 1 respect to the :diilerentiated .wave 38 :are shown1 1 11 .1arnplier-:|2.. The pulses E5; appearing the in Figs. 6,.'7. and .8. 1 1 1 1 1 .1

1 1 1 videolfrequency ampliier cutputare applied to E 1 1 1 Thezsine wave-oscillator1281inth'e example be- 1 1 1. 1 one of the Vertical deilecting plates. i3 and i3d 1 1 ing described -is .oi1 the.' resistofr-1capaci1tor1r type 1 1 1 1 of1 a cathoderay indicator tube1 541.1 1 1 11:5 which is specially: designed to obtain unusually1 1 good frequency stability; :Referring toFig. 2, the 1 1 I l oscillator 1281 comprises: ia lrst1r vacuum. tube 5l 1 the tube iis coupled back; tothe inputcirouit of 1 1' -1 1 1 the tube: 5lA to: provide :regenerative 1 feedback 1 1 througha coupling :capacitor 541 and :through a 1 1 frequency :selective network whichcomprises rie-1 1 11 i 1 l 1 1 :sistors andlandacapacitor 'azco'nnected 'in 1 l 1 1 1' 1 kseriesilith 1each :other and also connected in se-` 1 1 1 1 1 riesv withresistors. l,- 6;2,: 16.3 which areshunted 1 1 1 1 1 1 1 by a capacitor te and asmail adjustable capaci-1 i i 1 1 1 1 1 1 ztor; 64.. i Additional capacitors 64a, 64o. .etc;, ci 1 1 1 i 1 1 :different values maybefconneoted in1paral1el1with i 1 1 1 1 1 1 plate ldforseparating the slow sweep trace; 26 1 1 1 fromi the iast sweeptrace 211.; i r 1 1 1 1 1 1 1 1 301 `capa.titers @it and 64* .by means of: the switch. 215 i 1 1 1 1 1 1 1 The circuit 1for' producing the say/tooth. wave 1 1 1to: lnakel theioSCllatOI1ope1'ate at any-oneioff a 1 1 1 1 1 11i-andthe reetangularpulses 123 zwill now bede- 1 1 1 1blu-Talita of; predeterminedfrequencies. 1 1 1 1 1 1 I 1 1 1 1 1 1 1 f 1 1 scribed.A 1A:answers-oscillator128; whichmay be 1 1 1 The Cath'de'lad @f1 the 5111061512 may 'olude a1 1 1 l 1 1 1 1 1 1 .switched toidiierentirequency settings by .means 1 1 1 tungsten filament. lamp 15ior any similar means 1 1 1 1era. switch 291,2app1ies a .sine-wave voltage 3e tot 351 1ieristabiliziusor:controlling theamplitude' of oS- 1 I 1 1 1 1 1 1 1 :a: pair :ofvacuum tubes .Si -and1321 connected in 1 Sina/10H51 by negative ibedbackl.1 :The negative I 1 cascade and: adjusted to fclip the sine waveisuc`1 1 1 1 1 feedback connection also includes a resistor 68' 1 i 1 1 1 1 1 1 .cessivelyl thus producing' the 1voltage pulses 133 1 1 1 1 :GOmected zfromthe. coupling capacitor i511 tothe 1 1 1 `1 andes. r -1 111: 1 1. 1 1 w1 -1`iunotion1pointofthelamptlzandthecathodeof-11111 1111lhe: pulsesit produceiarcurrentdow through 1.11131 the tube 5l,.1;1The:output of the'oscillator' 28 1 -takenioi :a resistor .Ei91'in1the1cathode leadof the- 1 1' 1 1 1 1 :a diiilerentiatiing' circuit comprising capacitor 1 1 1 i5 and a resistor 3l to produce the Voltage wave 38 across resistor 3l. The time relations of the waves 3i). 35 and Sil are shown in Figs. 3, 4 and 5. The voltage 38 is applied through a resistor 3S to the grid of a vacuum tube il with suicient amplitude to drive the grid positive whereby the voltage 38 is clipped and appears on the grid as shown at l2 with flat-topped portions. In the present example, each iiat portion is 5000 micro- 1 seconds long, this being the duration of the desired fast sweep.

The cathode circuit of the tube @l includes a capacitor i3 which is shunted by the resistor potentiometer 2l. Voltage is applied to the anode of tube lll through an anode resistor 44. During each positive flat-topped portion of the wave l2 there is anode current flow through the tube lll which charges the capacitor i3 whereby the steep portion of the sawtooth wave il (Fig. 7) is produced. Following the flat-topped portion the capacitor 43 discharges through the resistor 2i whereby the gradual sloping portion of the sawtooth wave l'i is produced. As previously described, the wave l? is amplied and applied to the horizontal delecting plates lli and 56a.

During each 5G09 ,u second charging period of capacitor e3, a 5000 u second pulse appears at the anode of tube 4l as indicated at 315. The pulses i5 are applied through a coupling capacitor ll and a resistor lla to a clipping tube A18 whereby the rectangular pulses 23 are obtained. As pre viously explained, the pulses 23 are applied to a vertical deflecting plate to separate the slow and fast traces. Center marking pulses (Fig. 8)

tube 52.

It will be noted that the second tube 52 is connected to function as a triode although a pentode normally is used. It was found that the use of a triodein the circuit as illustrated improved the frequency stability by a Very large amount.

The operation of the system will now be more fully described with reference to Figs. 9 to 10a. Fig. 9 shows the slow and fast cathode ray traces, 26 and 2l, respectively, where the A pulses indicated at I5 fromY the A transmitter station together with two echo pulses A and A" appear on the slow trace 26. Fig. 9a is similar to Fig. 9 but shows the pulses A, A' and A on the .fast trace 2l where they are well separated. The procedure is first to adjust the sine wave oscillator 28 until the pulses appear on the slow trace 26 and then to let them drift around until they appear on the fast trace 2"! where they are held stationary by properly adjusting the ire quency of oscillator 28.

It is, of course, necessary to know which transmitter of the several pairs of A and B stations is being received. Since the pairs of stations transmit at diierent pulse repetition rates, a particular pair of stations is identified by that position of the station selecting switch 29 on the oscillator 28 which makes the pulses either stand still or drift slowly en one of the cathode ray traces 216 or 2. Then the station of the known pair of A and B stations is identified by holding a pulse at the left end of the 1cathode ray trace 26 as shown in Figs. 10a and 10b. If, as in Fig. 10a, the second pulse on the trace is at the right of the center mark 'H (produced by pulse 50) it is the pulse B from the B station; if, as in Fig. b, it is at the left of mark ll, it is the pulse A from the A station. The reason for this will be apparent by comparing Figs, 10a and 10b with Fig. 10 where the sequence of transmission of the A and B pulses is illustrated. Since the B pulse occurs a little later than midway between successive A pulses, the above described identication is possible. After the pulse has Ibeen identied and held stationary on the fast trace 21, the receiver loop l0 is turned to the position that reduces the amplitude of the identied pulse to a minimum.

Figs. 10c and 10d illustrate how the pulses are caused to appear on either the slow trace or the fast trace as desired. After the correct station selection has been made by means of the switch 29 (which has a control knob 19) the oscillator frequency may be changed slightly by turning the fine adjustment knob 13 which varies the capacity of the small capacitor 64'. Thus, the phase relation of the sawtooth wave Il with respect to the pulses is allowed to change (whereby the pulses appear to drift on the trace) until the pulses occur either during the slow sweep or during the fast sweep as desired, these two phase relations being shown in Figs. 10c and 10d, respectively. The oscillator frequency is then adjusted by the knob 13 to exact synchronism with the pulse frequency whereby the pulses remain stationary on the desired trace. Thereafter the loop is adjusted to obtain a null which indicates the direction of the transmitter, or more exactly, the Wave front of the radio wave from the transmitter.

We claim as our invention:

1. Receiving apparatus for receiving radio pulses, said apparatus comprising a pulse receiver, a cathode ray indicator tube having a horizontal deflecting means and a vertical deflecting means, means for producing a sawtooth dele'cting wave which may be made to recur in synchronism with the received pulses, said sawtooth wave having a gradually sloping portion and a steepreturn-line portion, means for applying said sawtooth wave to said horizontal deilecting means, means for producing periodically recurring electrical pulses each of substantially the same duration as one of said sawtooth wave portions and occurring simultaneously therewith, means for applying said last pulses to said vertical deecting means whereby the fast cathode-ray trace produced by said return-line portion and the slow trace produced by said gradually sloping portion are separated, means for producing an indication on one of said cathode-ray traces in response to the reception of a pulse, and means for adjusting the relative phase of said sawtooth wave and the received pulses wherebv the pulse indication may be made to occur on either the slow trace or the fast return-line trace as desired.

2. In a pulse direction finder system, means including a directive antenna for receiving radio pulses transmitted from a known transmitter station, a cathode ray indicator tube having a horizontal deflecting means and a vertical deecting means, means for producing a sawtooth deecting wave which may be made to recur in synchronism with the received pulses, said sawtooth wave having a gradually sloping portion and a steep return-line portion, means for applying said sawtooth wave to said horizontal deecting means, means for producing periodically recurring electrical pulses each of substantially the same duration as said return-line portion and occurring simultaneously therewith, means for applying said last pulses to said vertical deilecting means whereby the fast cathode-ray trace produced =by said return-line portion is separated from the slow trace produced by said gradually sloping portion, means for producing an indication on one of said cathode-ray traces in response to the reception of a pulse, and means for adjusting the phase of said sawtooth wave with respect to the received pulses whereby the pulse indication may be made to occur on either the slow trace or the fast returnline trace as desired.

3. In a pulse direction linder system, means including a directive antenna for receiving radio pulses transmitted from a known transmitter station, a cathode ray indicator tube having a horizontal deflecting means and a vertical deilecting means, means for producing a sawtooth delecting wave which may be made to recur in synchronism with the received pulses, said sawtooth wave having a gradually sloping portion and a steep return-line portion, means for applying said sawtooth wave to said horizontal deflecting means, means for producing periodically recurring electrical pulses each of substantially the same duration as said return-line portion and occurring simultaneously therewith, means for applying said last pulses to said vertical deecting means whereby the fast cathode-ray trace produced by said return-line portion is separated from the slow trace produced by said gradually sloping portion, means for producing an indication on one of said cathode-ray traces in response to the reception of a pulse, means for adjusting the phase of said sawtooth wave with respect to the received pulses whereby the pulse indication may be made to occur on either the slow trace or the fast returnline trace as desired, and means for producing a center mark indication on said slow trace at its midpoint.

4. In a pulse direction finder system, means including a directive antenna for receiving radio pulses transmitted from a known transmitter station, a cathode ray indicator tube having a pair of horizontal deecting plates and a pair of Vertical deecting plates, means for producing a sawtooth deecting wave which may be made to recur in synchronism with the received pulses, said sawtooth wave having a gradually sloping portion and a steep return-line portion, means for applying said sawtooth wave t0 said horizontal deecting means, means for producing periodically recurring electrical pulses each of substantially the same duration as said return-line portion and occurring simultaneously therewith, means for applying said last pulses to one of said vertical deflecting plates whereby the fast cathode-ray trace l produced by said return-line portion is separated from the slow trace produced by said gradually sloping portion, means for applying the received pulses to the other vertical deflecting plate to produce an indication cn one of said cathode-ray traces in response to the reception of a pulse, and means for adjusting the phase of said sawtooth wave with respect to the received pulses whereby the pulse indication may be made to occur on either the slow trace or the fast returnline trace as desired.

BENJAMIN SHMURAK. GEORGE D. HULST, Jn. 

